Gas geochemistry of the Cordón Caulle geothermal system, Southern Chile

The Cord´on Caulle geothermal system is located in a NW-trending volcano-tectonic depression of the Southern Andean Volcanic Zone of Chile. Outflows of low chloride water were previously interpreted as the surface expression of a shallow steam-heated aquifer, with subsurface temperatures of 150–170 ◦C. Gas data from fumaroles and hot springs have been used to assess the nature and temperature of the deeper, underlying geothermal reservoir. Fumaroles at the northeastern border of Cord´on Caulle have 3He/4He ratios typical of subduction margins (6–7 RA) and N2/Ar ratios of about 40, indicating deep convection of air-saturated groundwater. Fumaroles at the southwestern border haveN2/Ar ratios >300, suggesting the presence of a deep volcanic component. Gas ratios of fumarole discharges yield equilibration temperatures >300 ◦C, whereas those of hot spring waters suggest temperatures of about 160 ◦C. Based on these data, and comparisons with well documented liquid and vapor-dominated geothermal systems, a model is proposed of a boiling liquid-dominated geothermal system overlain by a secondary steam-heated aquifer. © 2007 CNR. Published by Elsevier Ltd. All rights reserved